CH702576A2 - Micro-mechanical piece such as an anchor and an escape wheel for a timepiece, comprises a core made of silicon, a first coating layer comprising diamond, a second coating layer on the first layer, and an intermediate layer - Google Patents

Abstract

The micro-mechanical piece (101) comprises a core (103) made of silicon, a first coating layer (105) comprising diamond, a second coating layer (201) on the first layer, partially covering the first layer and having tribological properties complementary to those of the first layer, and an intermediate layer between the core and the first coating layer. The first layer has a thickness of 0.5-5 mu m, and the second layer has a thickness of 50-1000 nm. The surface of the core is partially coated with the first layer. An independent claim is included for a process for manufacturing the micro-mechanical piece.

Description

FIELD OF THE INVENTION

The invention relates to a micro-mechanical part, such as a timepiece, made of silicon and having a coating. The invention also relates to a method of manufacturing said micromechanical part.

STATE OF THE ART

[0002] Silicon (Si symbol) is a chemical element of the family of crystallogens. It is the most abundant element in the earth's crust after oxygen. It does not exist in the free state, but in the form of compounds: in the form of silicon dioxide (SiO2), silica (in sand, quartz, cristobalite, etc.) or other silicates.

[0003] Silicon has, in the pure state, high mechanical characteristics which make it possible to use it for the production of small parts intended for certain micromechanisms and even for the manufacture of spiral springs intended for high-end mechanical watches. In the context of the present invention, silicon parts are understood to mean parts etched by a deep reactive-ion etching (DRIE) process, especially for watchmaking, such as anchors, escape wheels or any other component.

Silicon is a material increasingly used in the manufacture of micro-mechanical parts. Compared to metals or alloys conventionally used to manufacture micro-mechanical parts, such as articulated parts, gears or springs, silicon has the advantage of having a density 3 to 4 times lower and therefore of have a very low inertia, and be insensitive to magnetic fields. These advantages are particularly important in the field of watchmaking, both as regards isochronism and the running time when the energy source is constituted by a spring.

Silicon, however, has a disadvantage of being sensitive to shocks, which may be necessary during assembly, unavoidable during operation, or fortuitous during use, if for example the user drops his watch. bracelet. To overcome the weaknesses of silicon, solutions are known where the silicon parts are at least partially coated with diamond. The manufacture of silicon-coated silicon parts provides rigidity and mechanical resistance to silicon. By diamond is meant a deposition of a diamond coating on silicon (diamond coated silicon) and non-diamond crystallized diamond-like carbon (DLC).

The diamond however has the following disadvantages: its extreme hardness makes it becomes incompatible with other materials in friction. This incompatibility is due to the abrasion caused by the diamond on the material in contact. Diamond also has a disadvantage of having poor tribological properties found in the specific operation of anchors and escape wheels. Both components are made of silicon and covered with diamond. By tribology, we mean the science that studies the phenomena likely to occur between two material systems in contact, motionless or animated relative movements. It covers, among other things, all areas of friction, wear and lubrication.

Solutions are also known in which the silicon is coated with a layer of silicon dioxide. This solution has great advantages in terms of tribological properties but the part is not mechanically reinforced.

SUMMARY OF THE INVENTION

The present invention therefore aims to provide a micro-mechanical part which has no disadvantages of known parts and which is also particularly suitable for use in the field of timepieces.

For this purpose, the subject of the invention is, according to a first aspect, a micro-mechanical part comprising a core made of silicon, in which the micro-mechanical part comprises a first coating layer, the first layer comprising diamond, characterized in that the micro-mechanical part comprises a second coating layer on the first layer, the second layer at least partially covering the first layer, and having tribological properties complementary to those of the first layer.

The micro-mechanical part according to the present invention is very rigid thanks to the diamond coating but has ideal tribological properties thanks to the second coating. The second coating makes the micro-mechanical part compatible with other friction materials and the abrasions can be avoided.

According to a particular embodiment, the micromechanical part is such that at least one intermediate layer is arranged between the core and the first coating layer. Thus, the silicon core and this at least one intermediate layer forms an assembly that can be coated with additional layers. The intermediate layer or layers may also be made of a crystalline material, in particular silicon. But it is of course possible to make these intermediate layers in other materials.

With these intermediate layers, the micro-mechanical part has advantageous properties compared to a part in which the core is directly coated with the diamond layer. For example, the intermediate layers may be useful for having an extremely low roughness. Or else the intermediate layers can be put to facilitate or guarantee the adhesion of the diamond.

The subject of the invention is, according to a second aspect, a method for manufacturing a micro-mechanical part, comprising the following steps: engraving a silicon core of the micro-mechanical part; depositing a first coating layer, the first layer comprising diamond, and at least partially covering the core, characterized in that the method further comprises: depositing a second coating layer on the first layer, the second layer at least partially covering the first layer, and having tribological properties complementary to those of the first layer.

Other aspects of the present invention are in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood on reading the following description given by way of non-limiting example, by looking at the attached drawings which show schematically: <tb> - fig. 1 <sep> a sectional view, a micro-mechanical part according to a known solution of the state of the art, and <tb> - fig. 2 <sep> a sectional view, a micro-mechanical part according to an embodiment of the present invention.

DETAILED DESCRIPTION OF AN EMBODIMENT

The same reference numbers indicate the corresponding elements in the different figures.

Referring to the drawings, a non-limiting embodiment of a micro-mechanical part and its manufacturing method according to the present invention is now explained in more detail.

[0018] FIG. 1 illustrates a sectional view of a micro-mechanical part 101 such as an anchor in the field of watchmaker. This part comprises a core (main part) of silicon 103, all or part of the surface is coated with a diamond layer 105. The core 103 is obtained for example by deep reactive ion etching. Deep reactive ion etching is a highly anisotropic reactive ion etching process used in microelectronics. It creates holes and deep trenches in wafers with a width-to-height ratio of 20: 1 or more. This technique has been developed, for example, for electromechanical microsystems that require this type of functionality. There are two main high-rate DRIE techniques: cryogenic and Bosch.

To obtain the diamond layer 105, a DCS deposit is made. Normally, a diamond layer 105 whose thickness is between 0.5 μm and 1 μm is sufficient to guarantee the desired rigidity of the micromechanical part 101.

To improve the tribological properties of the micromechanical part 101 and thus to avoid the disadvantages of abrasion, the diamond layer 105 is covered either partially or entirely with an additional layer 201 (FIG. characteristics: good diamond adhesion and good tribological properties. In this example, this additional layer 201 is silicon oxide. The thickness of this additional layer (201) is normally between 50 nanometers and 1000 nanometers.

According to a first example, the additional layer 201 is obtained by a silicon oxide deposition by plasma-enhanced chemical vapor deposition (PECVD) process or equivalent method on diamond. Plasma enhanced chemical vapor deposition is a process used to deposit thin layers on a substrate from a gaseous (vapor) state. Chemical reactions take place during the process after the formation of a plasma from the reactor gases. The plasma is generally created from this gas by radio frequencies or by an electric discharge between two electrodes. A plasma is a gas in which a high percentage of atoms or molecules are ionized.

Plasma deposition is frequently used in the manufacture of semiconductor devices for depositing films on wafers having one or more metal layers or other temperature sensitive structures. Silicon oxide (for example silicon dioxide, SiO2) can be deposited from dichlorosilane or a mixture of silane and oxygen, generally at pressures ranging from a few hundred millitorrs to a few torrs.

In a second example, the additional layer 201 is obtained by depositing polysilicon on the diamond by the same methods as in the first example. In this case, oxidation of the polysilicon in an oven allows transformation into silicon oxide. In other words, thermal oxidation is carried out for the high temperature polysilicon, normally between 800 ° C. and 1300 ° C. to obtain a layer of silicon oxide 201 on the diamond.

Polysilicon, very commonly called polycrystalline silicon or poly-Si is a form of silicon that differs from monocrystalline silicon as amorphous silicon. Unlike the first, composed of a single crystal and the second having no or very weak crystallographic coherence, the polysilicon consists of multiple small crystals of various sizes and shapes, and therefore has properties different from the other two forms. Unlike monocrystalline silicon, polysilicon is composed of a very large number of small crystals or crystallites of silicon.

Other overlays, such as tantalum oxide (Ta2O5) or silicon nitride, could also be envisaged, provided that their adhesion to silicon is sufficient and that these overlays have good tribological properties. The final layer 201 may also be a mixture of the materials identified above. In the solution described above the two final coating layers 105; 201 are deposited directly on the core 103. One can also consider solutions where there is one or more intermediate layers between the core and the final layers 105; 201.

Claims (15)

A micro-mechanical part (101) comprising a core (103) made of silicon, wherein the micro-mechanical part comprises a first coating layer (105), the first layer (105) comprising diamond, characterized in that the micro-mechanical part (101) comprises a second coating layer (201) on the first layer (105), the second layer (201) at least partially covering the first layer (105), and having tribological properties complementary to those of the first layer (105). The micro-mechanical part (101) according to claim 1, wherein at least one intermediate layer is arranged between the core (103) and the first coating layer (105). The micro-mechanical part (101) according to any one of the preceding claims, wherein the second layer (201) is a silicon oxide layer, a tantalum oxide layer, a silicon nitride layer. or a mixing layer of these materials. 4. Micro-mechanical part (101) according to any one of the preceding claims, wherein the micro-mechanical part (101) is a timepiece. 5. Micro-mechanical part (101) according to claim 4, wherein the timepiece is an anchor or an escape wheel. The micro-mechanical part (101) according to any one of the preceding claims, wherein the thickness of the first layer (105) is between 0.5 micrometers and 5 micrometers. The micro-mechanical part (101) according to any one of the preceding claims, wherein the thickness of the second layer (201) is between 50 nanometers and 1000 nanometers. The micro-mechanical part (101) according to any one of the preceding claims, wherein the web surface (103) is at least partially coated with the first layer (105). 9. A method of manufacturing a micro-mechanical part (101), comprising the following steps: etching a silicon core (103) of the micro-mechanical part (101); depositing a first coating layer (105), the first layer (105) comprising diamond, and at least partially covering the core (103), characterized in that the method further comprises: depositing a second coating layer (201) on the first layer (105), the second layer (201) at least partially covering the first layer (105), and having tribological properties complementary to those of the first layer (105) . The manufacturing method according to claim 9, wherein at least one intermediate coating layer is deposited on the core (103) before depositing the first coating layer (105). 11. The manufacturing method according to any one of claims 9 or 10, wherein the etching is performed by deep reactive ion etching. The manufacturing method according to any one of claims 9 to 11, wherein the first layer (105) is deposited as a diamond coating on the silicon. 13. The manufacturing method according to any one of claims 9 to 12, wherein the second layer (201) is silicon oxide and is obtained by plasma-assisted chemical vapor deposition. 14. The manufacturing method according to any one of claims 9 to 13, wherein the second layer (201) is obtained by depositing polysilicon on the first layer (105) by plasma-assisted chemical vapor deposition and performing subsequent thermal oxidation at a temperature between 800 ° C and 1300 ° C to convert the polysilicon to silicon oxide. 15. Manufacturing method according to any one of claims 9 or 11 to 14, wherein the first layer (201) is deposited directly on the core (103).